There has been known a traffic control system for improving smooth running of vehicles at an intersection or the like. In the traffic control system, a roadside unit that wirelessly transmits roadside unit information is installed at an intersection. The roadside unit information includes traffic-light information representing a command (a stopping command or a running command) provided to the vehicles by a traffic light. Each of the vehicles can control its own running in response to the command provided by the traffic light by receiving the roadside unit information from the roadside unit.
In the traffic control system, a vehicle wirelessly transmits vehicle information including the running state and the like of the vehicle to other vehicles, and wirelessly receives vehicle information including the running state of other vehicles from these vehicles. Due to this configuration, the vehicle can notify other vehicles behind of the running state of the vehicle, and can control the running of the vehicle corresponding to the running state of other vehicles in front.
In the traffic control system, the roadside unit and the vehicle transmit information to the same channel (the same frequency band). Therefore, when the vehicle is transmitting running information or the like, the vehicle cannot receive information transmitted from other vehicles or from the roadside unit. Further, in a case where the roadside unit and the vehicle simultaneously transmit information, an interference occurs, and any vehicle cannot receive the information from the roadside unit in this case. However, when the vehicle enters into a communication area where information can be received from the roadside unit, it is desirable that the vehicle can receive information from the roadside unit reliably and more quickly.